Pipe strings supported in earth bore holes by drilling rigs are engaged by static spiders on drilling floors and by vertically movable elevators suspended by bails from traveling blocks of the rigs main hoisting gear. In many cases, there is little difference between spiders and elevators. Such arrangements are well known to those skilled in the related art.
When practical, it is desirable to support pipe strings that are vertically suspended in earth bore holes by engagement of plane surfaces on the pipe strings. When the pipe string has to be positioned with connections some distance above the usual drilling floor spider, for instance, there is usually no abutment available for the spider to grip.
To grip the cylindrical surface of the pipe, the spider, or elevator, is usually equipped with a plurality of slips distributed peripherally about the pipe and supported by a tapered slip bowl in the spider, or elevator, bore. The tapered bowl converts vertical pipe load to radial force that thrusts the slips against the pipe surface. The slips carry teeth, usually on an attached die, that bite into the pipe surface to provide the needed slippage resistance to support the pipe load. Ideally, the dies are so designed that they do as little damage to the pipe as possible without inviting slippage.
Pipe gripping dies are normally used in, vertically distributed, sets of three or more on each slip. The dies tend to slide downward on the supporting slips to which they are attached. In prior art, the dies rest one atop the other and the downward force on each die bears upon any die below. The cumulative load then is supported by abutment features on the related slip. The abutment feature can be overloaded and can deform the slip. In some cases, the pipe load has been dropped into the well with serious consequences. There is advantage in providing a discrete supporting abutment surface for each die to prevent the load accumulating on another abutment surface below.